Re: [Qemu-devel] [PATCH 0/3] QEMU logging improvements

[Kashyap Chamarthy <kchamart@redhat.com>]

On Thu, Oct 15, 2015 at 10:30:21AM +0300, Denis V. Lunev wrote:
> The following is done:
> - QMP/HMP events are now logged

I applied this patch series locally, and tried to test it the below way:

Launch a minimal QEMU instance:

  $ /home/kashyapc/build/build-qemu-upstream/x86_64-softmmu/qemu-system-x86_64 \
   -nographic                      \
   -nodefconfig                    \
   -nodefaults                     \
   -m 2048                         \
   -cpu SandyBridge                \
   -device virtio-scsi-pci,id=scsi \
   -device virtio-serial-pci       \
   -drive file=./cirros.qcow2,if=virtio,cache=writeback \
   -serial stdio \
   -D ./output-of-qemu.txt \
   -qmp unix:./qmp-sock,server
    
And, issued QMP commands via `qmp-shell`:

  $ ./qmp-shell /export/qmp-sock
  Welcome to the QMP low-level shell!
  Connected to QEMU 2.4.50
  (QEMU)
  (QEMU) query-status
  {"return": {"status": "running", "singlestep": false, "running": true}}
  (QEMU)
  (QEMU) blockdev-snapshot-internal-sync device=virtio0 name=snapshot1
  {"return": {}}

As we can see, the QMP commands gets successfully invoked, but nothing
gets logged to the output-of-qemu.txt file.  Maybe because everything is
logged onto my stdout of qmp-shell?

A couple of related questions:

  - Is the way I supplied '-D' option correct?  If so, why the
    output-of-qemu.txt file does not get created?  _Should_ it?

  - If I `touch output-of-qemu.txt`, then re-try issuing QMP commmands
    from 'qmp-shell', still, nothing gets logged to it.  Probably
    because only stderr is supposed to get logged to '-D logfile'?

Do I have to turn on any other special knob to take advantage of
LOG_CMD/LOG_TIME flags mentioned in your patch[1]?

I'm pretty sure I'm missing something. . .

[1] http://lists.nongnu.org/archive/html/qemu-devel/2015-10/msg03316.html

> - timestamp is added to the log message
> - arguments of qemu_log/qemu_log_mask are not calculated now if the log
>   is disabled
> 
> These patches are sent in the hope that it is not too late for QEMU 2.5.
> 
> Logging subsystem in QEMU looks rudimentary to me and should be definitely
> improved, f.e. log on stalled NFS could ruin the system completely. Anyway,
> it is too late for this at the moment.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Pavel Butsykin <pbutsykin@virtuozzo.com>
> CC: Markus Armbruster <armbru@redhat.com>
> CC: Luiz Capitulino <lcapitulino@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> CC: Peter Maydell <peter.maydell@linaro.org>
> 
> 

-- 
/kashyap